Enable Sphinx viewcode extension (links to source code)

Author: Phil Rzewski

doc/conf.py

@@ -30,7 +30,7 @@
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
-extensions = ['sphinx.ext.autodoc']
+extensions = ['sphinx.ext.autodoc', 'sphinx.ext.viewcode']
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']